A gas spinning at sonic velocities has an effectively higher heat capacity, which can be used to modify engine fuel cycles. A remarkable gain in fuel efficiency is shown to be theoretically possible for the Otto and Diesel cycles. Neglecting inefficiencies in producing the spinning, the theoretical maximum fuel efficiencies of Otto cycle engines might be increased by as much as 10%-40% at conventional engine temperatures. Low-temperature, clean-burning engine cycles might, in principle, benefit even more from a spinning working gas. The new limit neglects such non-ideal effects as friction, insufficient mixing, or heat transfer, but if successful, would suggest transformative technology.
In using spinning gas in an engine, the spin must be rapid enough to affect the moment of inertia of the gas. That would equip the gas with higher heat capacity, leading to potentially very large benefits in efficiency. This rapid spinning is very different from the modest spinning that people have suggested for controlling say the mixing of the fuel. The main technological hurdles in rapid spinning involve initiation of the spinning, efficient recovery of the spinning energy, and control of turbulence.
By exploiting rotation-dependent heat capacity, a possibility that had never been considered, a radically new invention in the field of thermal cycle internal combustion engines is possible. None of the practical engine cycles, such as Otto cycle, Diesel cycle, Miller cycle or Atkinson cycle, employ anything like such an effect.